Olfactory sensation begins when odorants interact with odorant receptors in the nasal epithelium. The chemical signal is transformed into an electric spike signal, before being sent to the thousands of glomeruli near the surface of the olfactory bulb. Importantly, odor signals associated with the same odorant receptors converge to a few glomeruli and each glomerulus represents a single odorant receptor. Therefore, it has long been assumed that a single glomerulus and all associated neurons compose a discrete functional module, which mediates the processing of odor information associated with a given type of odorant receptor. However this hypothesis has not been directly tested, owing to the technical difficulties of simultaneously visualizing and detecting the activity of each neuron within a module. In this proposal, we employ recently developed transgenic mouse lines, neuronal labeling by single glomerular electroporation and in vivo two-photon optical imaging techniques. Our goals are to reveal the structural and functional organization of the glomerular module and to determine the interaction between adjacent modules, focusing on the following specific aims; 1) Determine the cell-type specific anatomical and functional configuration of a single glomerular module. 2) Quantify the spatiotemporal activity patterns of multiple modules in response to single odorants and mixtures of odorant molecules. The results gained from these studies will highlight the fundamental rules that underlie information processing in glomerular circuits and will help to reveal the mechanisms of odor processing in the olfactory bulb. Moreover, they will shed light on general principles that underlie information processing in other brain regions and will facilitate future studies that aim to combine the analysis of network dynamics with single cell properties.